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Jeep J-20
3/4 ton, 1974–88

Factory gearing, tires, angles and brakes for the J-20, and what the usual upgrades do to it. Every number is from the maker's own figures unless the calculators say otherwise. A few figures here are still waiting on a factory document; the calculators mark them.

Use this truck in the calculators
130.7 in wheelbase · 29.9 in front · 43.9 in rear overhang
in
Axle ratio3.73–4.09Factory, by trim
Crawl ratio51.7:1Best trim: 360/401 V8, 1974-79, Dana 20 (8.00-16.5 tires)
Angles45 · 20 · 27°Approach, breakover, departure
Clearance8.1 inFactory figure
Highway mpg12EPA

Trims

3 we have figures for
TrimTireTransmissionAxleAnglesClearanceOpen
360/401 V8, 1974-79, Dana 20 (8.00-16.5 tires)30.0Borg-Warner T-18A 4-speed manual, GM Turbo Hydra-Matic 400 3-speed automatic3.73 / 4.0945 · 20 · 278.1 inUse →
Automatic with Quadra-Trac low range, 1974-79 (8.00-16.5 tires)30.0GM Turbo Hydra-Matic 400 3-speed automatic3.73 / 4.0945* · 20* · 27*8.1 inUse →
1980-88, part-time (8.75-16.5 tires)30.8Borg-Warner T-18A 4-speed manual, Chrysler TorqueFlite 727 3-speed automatic—45* · 20* · 27*8.1 inUse →

* The maker doesn’t publish this figure for that trim, so it shows the closest trim’s (same tire where we have one), or a close relative’s that shares the same body or front end. Hover the star to see which.

Size

Wheelbase
130.7 in
Front overhang
29.9 in
Rear overhang
43.9 in
Height
70 in
Body
Pickup
Stock tires
30.0, 30.8

Transmissions and low range

Borg-Warner T-18A 4-speed manual (wide ratio, 6.32 granny)
6.32 · 3.09 · 1.69 · 1
Chrysler TorqueFlite 727 3-speed automatic (V8)
2.45 · 1.45 · 1
GM Turbo Hydra-Matic 400 3-speed automatic
2.48 · 1.48 · 1
Low range, dana 20
2:1
Low range, quadra-trac bw1339 (with low range)
2.57:1
Low range, part-time (np208)
2.62:1

Axles

Front
Dana 44 (closed knuckle) - unverified
Rear
Dana 60 full-floating - unverified (fandom: 3/4 ton Dana 60)
3.73 ratio
360/401 V8, 1974-79, Dana 20 (8.00-16.5 tires), Automatic with Quadra-Trac low range, 1974-79 (8.00-16.5 tires)
4.09 ratio
360/401 V8, 1974-79, Dana 20 (8.00-16.5 tires), Automatic with Quadra-Trac low range, 1974-79 (8.00-16.5 tires)

Brakes

Front rotor
12.50 in, 318 mm
Front caliper piston
74.4 mm
Rear drum
12.00 in, 305 mm
Rear
drum (12 x 2.88 in)

Suspension

Front
solid axle on leaf springs
Rear
leaf springs, solid axle
Rear layout
Leaf springs

Fuel economy

EPA highway
12 mpg
Rated years
1985–1988, 4WD

Every calculator, set up for the J-20

Tire sizeBigger tires: speedo, clearance, angles and brakes.Compare tiresRegearHighway RPM on every ratio and mpg.Pick your gearsCrawl ratioHow slow it creeps, against other trucks.Work out crawlSpeedometerWhat it really reads on new tires.Fix your speedoLinksAnti-squat and what a lift does to it.Check your linksYour rigBuild sheet and measured angles.Start a build sheetLeaderboardsWhere the J-20 ranks against every stock truck.See where it ranks

Source: auto-brochures.com.

Use at your own risk. These calculators are here to help you plan and to inform your decisions, not to sign off on a build. Many numbers are estimates worked out from factory figures, and some factory figures are not yet confirmed. Check every number against your own truck, its manuals and a qualified shop before you buy parts, cut, weld, lift, regear or drive on it. Long Range Desert Tools is not liable for anything you do based on these calculators or their results. The full terms are in our policies.